Below are steps on how to create a content compliance rule.

1. Sign in to Admin panel

2. Google Apps > Gmail

3. Scroll down to Content compliance> Click on configure.

4. In select inbound, outbound, internal-sending and internal receiving.

5. On section 2. Add expressions that describe the content you want to search for in each message - click on add then select advance content match 

6.On option 3 select the option "Reject Message" then add a custom rejection message.

7.On option 4 deselect the bypass this setting option then save the above changes.